The present invention relates to a method of processing a high definition television signal for conveyance by way of a transmission channel or record carrier, said method comprising the steps of:
i) dividing a television picture into a plurality of adjacent blocks, PA0 ii) determining the degree of movement in each block, PA0 iii) categorizing each block into one of at least three categories with a first of said categories relating to blocks where the picture information is stationary or substantially stationary while other categories relate to blocks where the picture information exhibits various ranges of motion, PA0 iv) processing each block in a manner determined by the category in which it falls, PA0 v) calculating motion vectors for blocks of a second of said categories whose picture information exhibits movement within a first motion range, and PA0 vi) combining motion information in digital data form relating to motion vectors with the processed picture information to form a high definition television signal which digital data is allocated a given data capacity within the transmission capacity of said television signal. PA0 1. 80 ms branch with a field rate of 12.5 Hz applied for motion velocities ranging from 0 to 0.5 pixel per 40 ms. PA0 2. 40 ms branch with a field rate of 25 Hz applied for motion velocities ranging from 0.5 to 2 pixels per 40 ms. PA0 3. 20 ms branch with a field rate of 50 Hz applied for motion velocities greater than 2 pixels per 40 ms. PA0 i) dividing a television picture into a plurality of adjacent blocks, PA0 ii) determining the degree of movement in each block, PA0 iii) categorizing each block into one of at least three categories with a first of said categories relating to blocks where the picture information is stationary or substantially stationary while other categories relate to blocks where the picture information exhibits various ranges of motion, PA0 iv) processing each block in a manner determined by the category in which it falls, PA0 v) calculating motion vectors for blocks of a second of said categories whose picture information exhibits movement within a first motion range, and PA0 vi) combining motion information in digital data form relating to motion vectors with the processed picture information to form a high definition television signal which digital data is allocated a given data capacity within the transmission capacity of said television signal, PA0 vii) motion vectors are additionally calculated for blocks of a third of said categories whose picture information exhibits movement within a second motion range which differs to that of said first motion range, PA0 viii) that motion vectors calculated for the said second and third category blocks are dynamically allocated on the basis of picture content and said given data capacity, and PA0 ix) that the motion information in digital data form combined with the processed picture information relates to the dynamically allocated motion vectors for said second and third category blocks with the total motion information remaining within the said given data capacity. PA0 x) determining which of said stored motion vectors are relevant to the blocks of said second of said categories over a given period, PA0 xi) compiling a menu of said relevant motion vectors, and PA0 xii) combining said menu in digital data form with the processed picture information.
The invention also relates to apparatus for use with the above method.
Such a method is disclosed in the paper "Motion compensated interpolation applied to HD-MAC pictures encoding and decoding" by M. R. Haghiri and F. Fonsalas presented at the 2nd International Workshop on Signal Processing of HDTV, L'Aquilla, Italy, Feb. 29,-Mar. 2, 1988. In the method disclosed in that paper the television picture from a high definition source is subdivided into a plurality of blocks and each block is processed according to the degree of movement in the blocks. Processing is achieved by three parallel branches having different refresh times, one branch being for (substantially) stationary picture information while the other branches are for two different ranges of motion of the picture information. Details of the branches are given as:
The paper further describes that the 40 ms branch can be a motion compensated branch whereby motion vectors are generated according to the motion in blocks processed by that branch and the motion vectors used at the receiver for computing intermediate fields. Simulations on several natural television scenes revealed that with such a motion compensated scheme the motion velocity range for the 40 ms branch could be extended from 0.5 to 2 pixels per 40 ms to 0.5 to 6 pixels per 40 ms.
The above method formed a contribution to the work of a European research project EUREKA 95 on HDTV (high definition television) and this contribution eventually formed part of the HD-MAC coding system selected by that project. The selected coding system is described in the paper "HD-MAC coding for Broadcasting of High Definition Television Signals" by F. W. P. Vreeswijk as a contribution to the Club de Rennes Young Researchers' Seminar (Les Assises des Jeunes Chercheurs) at M. I. T. Cambridge, Mas., U.S.A., Oct. 9th to 13th , 1988. From this paper it will be seen that the motion velocity range for the motion compensated 40 ms branch covers from 0.5 to 12 pixels per 40 ms whilst the 20 ms branch is active for motion velocities greater than 12 pixels per 40 ms. In the selected coding system the transmitted number of samples is the same for each mode. In principle, halving the field rate allows the number of samples per frame to be doubled. The switching of modes is implemented on a block basis, because of the limited amount of DATV (digitally assisted television) data capacity. After subsampling, the 1250 lines signal from a high definition television source with line time of 32 .mu.s has to be converted to a 625 line signal with 64 .mu.s line time. This conversion is done by interleaving the HD samples of two consecutive intrafield HD lines. This technique is termed "line shuffling". In the HD decoder these samples are separated by a reciprocal "line de-shuffling" operation. Both encoder and decoder have three luminance coding branches, corresponding to the three modes. The three branches have three different spatial characteristics and therefore each branch has its subsampling scheme. The 40 msec. branch contains a motion estimator, which uses a block matching algorithm. The switching decisions come from a combination of both an "a priori" and an "a posteriori" decision scheme. There are only two chrominance coding branches: an 80 msec. branch and a 20 ms coding branch though this has subsequently been changed to add the third (40 ms) branch. No motion compensation is employed for the chrominance signal. The decoder derives the chrominance switching signal from the luminance DATV signal.
A branch switching signal will only have 5 possible temporal routes per basic 80 msec. period. The limitation follows from the observation that in a three branch system it is not useful to start a sub-sampling, using two or four fields, when the sub-sampling mode is changed before the two or four fields are really transmitted as this would cause severe alias to occur in the picture. The five temporal routes are:
______________________________________ field: 1 2 3 4 ______________________________________ Route 1: 80 80 80 80 Route 2: 40 40 40 40 Route 3: 40 40 20 20 Route 4: 20 20 40 40 ______________________________________
Before the coding operation a vector assignment is applied to limit the bit rate. In every first frame of an 80 msec. period all 169 possible vectors can be coded. In every second frame however, the best vector out of nine "neighbouring vectors" in the previous frame is selected and hence coded. If no vector is found the corresponding block will be transmitted in the 20 msec. mode. This results in the following possibilities:
______________________________________ fields 1/2 3/4 ______________________________________ Route 1: 80--80 1 Route 2: 40--40 169 .times. 9 Rotue 3: 40 - 20 169 Route 4: 20 - 40 8 Route 5: 20--20 1 1700 ______________________________________
In total there are thus 1700 possibilities per 80 msec. each of which can be coded with an 11 bit codeword. There are 6480 blocks per frame for a 1440 pixel by 1152 line active frame where the blocks are 16 pixels by 16 lines. Hence the bitrate is 891 kb/sec which is within the 1M bits per second allocation for this purpose.
With the selected coding system an 11 bit codeword is sent for each block per 80 ms which codeword is converted by means of a PROM at the decoder into a 2 bit block routing signal for the odd frame (BD-OFR), a 2 bit block routing signal for the even frame (BD-OFR), an 8 bit motion vector for the 40 ms blocks in the odd frame (MV-OFR) and a 4 bit motion vector relative address for the 40 ms blocks in the even frame (MV-EFR). The PROM contents are illustrated in the following table:
______________________________________ DATV Codeword BD-OFR BD-EFR MV-OFR MV-EFR ______________________________________ 1 80 80 -- -- 2 . . . 1522 40 40 1 . . . 169 1 . . . 9 1523 . . . 1691 40 20 1 . . . 169 -- 1692 . . . 1699 20 40 -- 1 . . . 8 1700 20 20 -- -- ______________________________________
It is an object of the invention to provide modifications of the above processing method.